1. Field of the Invention
This application generally relates to biological valve reinforcement devices, and, more particularly, to unstented biological heart valve reinforcement devices.
2. Description of the Related Art
Cardiac surgery often involves replacement of the patient's native valve with either a mechanical or biological (e.g., porcine, bovine, or homograft) valve.
A mechanical valvular prosthesis consists essentially of a mechanical valve device, such as a metal ball-and-cage or carbon bileaflet valve device, placed inside a ring covered by synthetic fabric. The ring facilitates incorporation of the device into the periphery of the orifice receiving the device. While mechanical prostheses have extremely long service lives, they present a significant clotting (thrombosis) risk and thus require the patient to undergo lifelong anticoagulation therapy. Furthermore, when mechanical valves do fail, the failure is likely to be catastrophic.
Biological valvular prostheses, on the other hand, comprise biological tissue taken from animals and treated by a suitable process so as to prepare them for implantation in the human body. Examples of biological valves include porcine aortic and mitral valves, porcine pulmonary valves, and aortic and mitral tissue valves that are reconstructed from a bovine pericardium. These valves have the advantage of a lower incidence of thrombosis, and thus minimize the need for prolonged anticoagulation therapy. Biological replacement valves further reduce the risk of catastrophic failure, as any problems that may occur tend to manifest symptomatically.
Biological valvular prostheses may either be stented or unstented. A stented valve comprises a biological tissue valve mounted on a metal or plastic frame (stent) which is covered by synthetic cloth. A stented design facilitates implantation of the biological prosthesis in that it requires only a single level of suture around its annular periphery. The tissue valve's position and configuration within the valve seat are maintained by the stent. An unstented biological valvular prosthesis, on the other hand, is not mounted on an external frame, but may be provided with synthetic cloth around the inflow opening. Implantation of unstented valves requires a more exacting surgical procedure than implantation of stented valves, due at least in part to the fact that unstented valves require more complex suturing in order to preserve the valve configuration once implanted. Furthermore, due to the geometry of the heart, unstented valves are generally restricted to use in the aortic position and are thus of limited application.